Field of the Invention
The present invention relates to a fuel cell formed by stacking a membrane electrode assembly and a metal separator. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes. A resin frame member is provided in an outer portion of the membrane electrode assembly.
Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes a solid polymer electrolyte membrane, an anode provided on one side of the solid polymer electrolyte membrane, and a cathode provided on the other side of the solid polymer electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is sandwiched between separators to form a power generation cell (unit cell). Generally, several tens to hundreds of unit cells are stacked together to from a fuel cell stack, e.g., for use in a vehicle.
In most cases, in order to supply a fuel gas and an oxygen-containing gas as reactant gases to the anode and the cathode of each of the stacked power generation cells, the fuel cell have so-called internal manifold structure. Therefore, for example, in order to achieve the desired sealing performance for preventing leakage of reactant gases, it is required to position and assemble the membrane electrode assembly and the separators accurately.
In this regard, for example, a fuel cell disclosed in Japanese Patent No. 4516279 is known. In the fuel cell, a gas diffusion layer of one of the electrodes of the membrane electrode assembly covers the entire surface of the electrolyte membrane, and a gas diffusion layer of the other of the electrodes of the membrane electrode assembly has a small surface size in comparison with the electrolyte membrane. A plurality of ridges for positioning the gas diffusion layer of the one of the electrodes and the outer end of the electrolyte membrane are present in a seal member provided integrally with the separator, and the ridges are spaced from one another.
Therefore, simply by engaging the membrane electrode assembly with the ridges of the separator, the membrane electrode assembly can be positioned relative to the separator accurately and easily.